1. Field of the Invention
The present invention relates to error resilience control techniques that can be applied to a compressed data transmission system in which data is encoded and sent from an encoding device and received and decoded by a decoding device. The techniques may be realized as a method or algorithm, the functionality of which can be embodied in an encoding device, e.g., a codec or encoder. The functions can be realized in the form of software, hardware, or combination thereof.
2. Description of the Related Art
In a packet-based or circuit-switched-based environment sometimes the compressed bit stream becomes corrupted as a result of bit or packet errors. In such situations, the video decoder associated with the receiver, upon determining that erroneous data has been received, typically implements a process known as error concealment. Error concealment generally involves replacing the missing or erroneously reconstructed video data by copying previously reconstructed video data that is stored in the receiver's buffer. Usually the previously reconstructed video data is the data of the previous frame.
There are disadvantages with such error concealment approaches. One disadvantage is error propagation and the lack of control over it. Because of the motion compensated prediction employed in the encoder, in order to reconstruct the next frame, information from a previous frame is used. However, if error concealment was employed for the previous frame, the current frame, when reconstructed, will have errors that have been propagated from two frames ago. This propagation may go on for several frames. In addition to causing error propagation, another disadvantage of error concealment schemes is loss of video quality. Schemes based on reducing the frame rate to combat packet losses also cause loss of video quality.
Attempts have been made to mitigate error propagation. For example, the encoder can be configured to encode in the intra-frame mode or an intra-macroblock refresh mode under certain conditions. Changing the reference picture selection has been proposed in H.264. While these techniques are generally effective, they also significantly increase the bit-rate of the codec.